Steel material for hot work tools

ABSTRACT

A steel material for hot work tools has an alloy composition that in weight-% essentially consists of: 0.3-0.4 C, 0.2-0.8 Mn, 4-6 Cr, 1.8-3 Mo, 0.4-0.8 V, balance iron and unavoidable metallic and non-metallic impurities, said non-metallic impurities comprising silicon, nitrogen, oxygen, phosphor and sulfur, the contents of which does not exceed the following maximum contents: max. 0.25 Si, max. 0.010 N, max. 10 ppm O, max. 0.010 weight-% P.

This application is a 371 of PCT/SE99/00217 filed Feb. 18, 1999.

TECHNICAL FIELD

The invention relates to a steel material for hot work tools, i.e. toolfor forming or working metals at comparatively high temperatures.

TECHNICAL POSITION

The term ‘hot work tools’ is applied to a great number of differentkinds of tools for the working or forming of metals at comparativelyhigh temperatures, for example tools for die casting, such as dies,inserts and cores, inlet parts, nozzles, ejector elements, pistons,pressure chambers, etc.; tools for extrusion tooling, such as dies, dieholders, liners, pressure pads and stems, spindles, etc.; tools forhot-pressing, such as tools for hot-pressing of aluminium, magnesium,copper, copper alloys and steel; moulds for plastics, such as moulds forinjection moulding, compression moulding and extrusion; together withvarious other kinds of tools such as tools for hot shearing,shrink-rings/collars and wearing parts intended for use in work at hightemperatures. There are a number of standard steel qualities used forthese hot work tools, e.g. AISI Type H10-H19, and also severalcommercial special steels. Table 1 presents some of these standardisedand/or commercial hot work steels.

TABLE I Nominal chemical composition by weight-percentage of known hotwork steels Steel Steel type no. C Si Mn Cr Mo W Ni V Co Fe W.nr1.2344/H13  1 0.40 1.0 0.40 5.3 1.4 — — 1.0 — Bal. W.nr 1.2365/H10  20.32 0.25 0.30 3.0 2.8 — — 0.5 — ″ W.nr 1.2885/H10A  3 0.32 0.25 0.303.0 2.8 — — 0.5 3.0 ″ W.nr 1.2367  4 0.38 0.40 0.45 5.0 3.0 — — 0.6 — ″W.nr 1.2889/H19  5 0.45 0.40 0.40 4.5 3.0 — — 2.0 4.5 ″ W.nr 1.2888  60.20 0.25 0.50 9.5 2.0 5.5 — 10.0 ″ W.nr 1.2731  7 0.50 1.35 0.70 13.0 —2.1 13.0 0.7 — ″ H42  8 0.60 0.30 0.30 4.0 5.0 6.0 2.0 ″ Com. 1*  9 0.350.1 0.6 5.5 3.0 — — 0.8 — ″ Com. 2* 10 0.32 0.3 0.6 5.1 2.6 — — 0.7 — ″Com. 3* 11 0.39 0.2 0.7 5.2 2.2 — 0.6 0.8 0.6 ″ W.nr 1.2396 12 0.28 0.400.45 5.0 3.0 — — 0.7 — ″ W.nr 1.2999 13 0.45 0.30 0.50 3.1 5.0 — — 1.0 —″ QRO ® 90* 14 0.39 0.30 0.75 2.6 2.25 — — 0.9 — ″ CALMAX ® * 15 0.280.60 0.40 11.5 — 7.5 — 0.55 9.5 ″ H11 16 0.40 1.0 0.25 5.3 1.4 — — 0.4 —″ Com. 4* 17 0.37 0.30 0.35 5.1 1.3 — — 0.5 — ″ Com. 5* 18 0.35 0.170.50 5.2 1.6 — — 0.45 — ″ *Commercially available, non-standard steel.QRO ® 90 and CALMAX ® are registered trademarks of Uddeholm Tooling AB.

DESCRIPTION OF INVENTION

In the first phase of the invention, the steels 1-15 in Table 1 werestudied. This study indicated that none of the steels studied satisfiedthe demands that can be placed on tools for all the different areas ofapplication mentioned above. Consequently, subsequent work concentratedon the development of an alloy primarily intended for die casting oflight metals, an area of application where there is a special need of anew steel material with a combination of properties that is better thanthat currently available using known steels. The objective of the steelmaterial in accordance with the invention is to offer optimal propertiesin terms of good hardenability and microstructure in order to providehigh levels of toughness and ductility also in heavy gauges. At the sametime there must be no deterioration of tempering resistance and hightemperature strength.

More particularly, a purpose of the invention is to offer a hot worksteel with a chemical composition that is such that the steel cansatisfy the following demands:

it must have good hot workability in order to thereby get a high yieldon manufacture,

it should be capable of manufacture in very heavy gauges, which meansthicker than e.g. 760×410 mm or thicker than Ø 550 mm,

it should have very low content of impurities,

it should not contain any primary carbides,

it should have good hot treatment properties, meaning inter alia that itshould be capable of being tempered at a moderately high austenitizingtemperature,

it should have very good hardenability, i.e. it should be capable ofbeing through-hardened even in the above-mentioned very heavy gauges,

it should be form-stable during heat treatment,

it should have good tempering resistance,

it should have good high-temperature strength,

it should have very good toughness and very good ductility properties inthe dimension ranges in question,

it should have good thermal conductivity,

it should not have an unacceptably large coefficient of heat expansion,

it should have good coating properties with PVD/CVD/nitriding,

it should have good spark erosion properties, good cutting and weldingproperties, and

it should have a favourable manufacturing cost

The above-mentioned conditions can be satisfied by the invented steelmaterial for the following reasons: firstly, by the steel alloy havingsuch a basic composition that the material can be processed in order toyield an adequate microstructure with very even distribution of carbidesin a ferritic matrix, suitable for further heat treatment of thefinished tool; secondly, by the steel material with the said basiccomposition also having the prescribed low contents of silicon, which isto be regarded as an impurity in the steel of the invention, and alsovery low contents of the non-metallic impurities nitrogen, oxygen,phosphor and sulphur. Indeed it has long been known that non-metallicimpurities, such as sulphur, phosphor, oxygen and nitrogen, involvecertain negative effects for many steels, especially regarding thetoughness of the steel. This also applies concerning the knowledge thatsome metals in trace element levels may have negative effects for manysteels, such as reduced toughness. For instance, this applies inrelation to titanium, zirconium and niobium at small levels.Nonetheless, it has not been possible in the case of most steels,including hot work steel, to improve toughness significantly solely byreduction of contents of impurities of this nature in steel. The studyconducted of existing steel alloys has also demonstrated that goodtoughness cannot be attained solely by optimising the basic compositionof the steel alloy. It was only possible to attain the said conditionsby a combination of an optimal basic composition and low or very lowcontents of the said non-metallic impurities, and also preferably a verylow content of titanium, zirconium and niobium.

In order to satisfy the above-mentioned conditions the invented steelmaterial has an alloy composition that by weight-percentage essentiallyconsists of:

0.3-0.4 C, preferably 0.33-0.37 C, typically 0.35 C

0.2-0.8 Mn, preferably 0.40-0.60 Mn, typically 0.50 Mn

4-6 Cr, preferably 4.5-5.5 Cr, suitably 4.85-5.15 Cr, typically 5.0 Cr

1.8-3 Mo, preferably max. 2.5 Mo, suitably 2.2-2.4 Mo, typically 2.3 Mo

0.4-0.6 V, preferably 0.5-0.6 V, suitably 0.55 V, balance iron andunavoidable metallic and non-metallic impurities, in connection saidnon-metallic impurities comprising silicon, nitrogen, oxygen, phosphorand sulphur, which may be included up to the following maximum contents:

max. 0.25 Si, preferably max. 0.20 Si, suitably max. 0.15 Si

max. 0.010 N, preferably max. 0.008 N

max. 10 ppm O, preferably max. 8 ppm O

max. 0.010 P, preferably max. 0.008 P, and

max. 0.010 S, preferably max. 0.0010, suitably max. 0.0005 S

It is preferable that titanium, zirconium and niobium occur in thefollowing maximum contents by weight-%

max. 0.05 Ti, preferably max. 0.01, suitably max. 0.008,

and most preferably max. 0.005,

max. 0.1, preferably max. 0.02, suitably max. 0.010,

and most preferably 0.005 Zr,

max. 0.1, preferably max. 0.02, suitably max. 0.010,

and most preferably max. 0.005 Nb.

As regards the choice of individual desirable alloy elements, it can bebriefly stated that the contents of carbon, chromium, molybdenum andvanadium have been chosen so that the steel should have a ferriticmatrix in the delivery condition of the material, a martensitic matrixwith adequate hardness after hardening and tempering, absence of primarycarbides but the existence of secondary precipitated carbides of MC andM₂₃C₆ type of sub-microscopic size in the hardened and temperedmaterial, while at the same time the basic composition of the steelshall provide potential in order to also attain the desired toughness.

The minimum content of chromium shall be 4%, preferably 4.5% andsuitably at least 4.85% in order that the steel should have adequatehardenability but may not be included at contents exceeding 6%,preferably max. 5.5% and suitably max. 5.15% in order that the steelshould not result in carbide content of type M₂₃C₆ and M₇C₃ to anundesirable extent after tempering. The nominal chromium content is5.0%.

Tungsten adversely affects thermal conductivity and hardenability inrelation to molybdenum and is therefore not a desirable element in thesteel but may be permitted in contents up to 0.5%, preferably max. 0.2%.However, the steel should suitably not contain any intentionally addedtungsten, i.e. the most desirable form of the steel only containstungsten at impurity levels.

Molybdenum should be included at a minimum content of 1.8%, preferablyat least 2.2% in order to provide adequate hardenability and temperingresistance together with the desirable high temperature strengthproperties. Greater contents of molybdenum than 3% carry a risk of grainboundary carbides and primary carbides, which reduce toughness andductility. Molybdenum should therefore not be included at highercontents than 3.0%, preferably max. 2.5%, suitably max. 2.4%. If thesteel contains a certain content of tungsten in accordance with theabove, tungsten partly substitutes molybdenum in accordance with therule “two parts tungsten corresponds to one part molybdenum”.

The steel shall contain a content of at least 0.4% vanadium to providean adequate tempering resistance and desired high temperature strengthproperties. Furthermore, the vanadium content should be at least thestated content to prevent grain coarsening when heat treating the steel.The upper limit for vanadium of 0.6% is set to reduce the risk offormation of primary and grain boundary carbides and/or carbonitrides,which would reduce the ductility and toughness of the steel. The steelshould preferably contain 0.5-0.6 V, suitably 0.55 V.

The steel should contain manganese in the stated levels, primarily toincrease the hardenability to some degree.

In order to utilise the potential good toughness that a steel materialwith the said contents of carbon, manganese, chromium, molybdenum andvanadium can provide, the contents on the said non-metallic impuritiesshould at the same time be held at the said low or very low levels. Thefollowing may be said regarding the significance of these elements ofimpurity.

Silicon can be found as a residual product in the steel from itsde-oxidation and may be included at a highest level of 0.25%, preferablymax. 0.20% and suitably max. 0.15% in order that the carbon activityshould be kept low and consequently even the content of primary carbidesthat can be precipitated during the solidification process, and, at alater phase, also the grain boundary carbides, which improves toughness.

Nitrogen is an element that tends to stabilise primary carbideformation. Primary carbonitrides, in particular carbonitrides in which,besides vanadium, titanium, zirconium and niobium may be included, aremore difficult to dissolve than pure carbides. These carbides, if theyare present in the finished tool, may have a major negative effect onthe impact toughness of the material. With very low contents ofnitrogen, these carbides are dissolved more readily on the austenitizingof the steel in conjunction with heat treatment, following which thesaid small secondary carbides, primarily MC and M₂₃C₆ type ofsub-microscopic size, i.e. less than 100 nm, normally 2-100 nm, areprecipitated, which is advantageous. The steel material according to theinvention should therefore contain max. 0.010% N, preferably max 0.008%N.

Oxygen in the steel forms oxides, which can initiate fractures as aresult of thermal fatigue. This negative effect on ductility iscounteracted by a very low content of oxygen, max. 10 ppm O, preferablymax. 8 ppm O.

Phosphor segregates in phase boundary surfaces and grain boundaries ofall kinds and reduces cohesion strength and consequently toughness.Phosphor content should therefore not exceed 0.010%, preferably max.0.008%.

Sulphur which by combining with manganese forms manganese sulphides, hasa negative effect on ductility but also on toughness because itinfluences transverse properties negatively. Sulphur may therefore existin an amount of max 0.010%, preferably max 0.0010%, suitably max.0.0008%.

Titanium, zirconium and niobium content ought not to exceed levels inthe steel higher than the maximum contents mentioned above, i.e. max.0.05% Ti, preferably max. 0.01, suitably max. 0.008 and most preferablymax. 0.005 Ti, max. 0.1, preferably max. 0.02, suitably max. 0.010 andmost suitably 0.005 Zr and max. 0.1, preferably max. 0.02, suitably max.0.010,and most preferably max. 0.005 Nb, in order to avoid the formationof nitrides and carbonitrides primarily.

In its delivery condition, the steel material according to the inventionhas a ferritic matrix with evenly distributed carbides, that aredissolved on the heat treatment of the steel in conjunction withhardening. On this heat treatment the steel is austenitized at atemperature between 1000 and 1080° C., suitably at a temperature of1020-1030° C. The material is thereafter cooled to room temperature andtempered one or several times, preferably 2×2 h, at 550-650° C.,preferably at approx. 600° C.

Further characteristics and aspects of the invention will be apparentfrom the following description of experiments conducted and from theappending patent claims.

BRIEF DESCRIPTION OF DRAWINGS

In the following description of performed experiments, reference is madeto the accompanying drawings, of which:

FIG. 1 is a three-dimensional diagram illustrating the nominal contentsof silicon, molybdenum and vanadium of a number of steels studied,

FIG. 2 shows the microstructure in soft-annealed state in the centre ofa steel of the invention,

FIG. 3 illustrates the tempering resistance of the examined steels,

FIG. 4 illustrates the influence on hardness of examined steel ofholding time at 600° C. after hardening and tempering,

FIG. 5 and FIG. 6 show a CCT diagram and TTT diagram respectively, for asteel of the invention,

FIG. 7 illustrates Charpy-V impact energy versus testing temperature ofsteels examined,

FIG. 8 and FIG. 9 illustrate the impact energy at +20° C. versus thethickness of tested plates with Charpy-V energy tests and tests withunnotched test specimens,

FIG. 10 is a diagram illustrating the hot ductility and hot yieldstrength of the examined steels, and

FIG. 11 is a schedule illustrating the property profiles of the examinedsteels.

DESCRIPTION OF EXAMINATIONS CONDUCTED

The chemical compositions of the examined steels are stated in Table 2

TABLE 2 Analysed chemical composition in weight percentage of steelsexamined Steel Steel type No. C Si Mn P S Cr Ni Mo W A A1 0.35 0.15 0.510.006 0.0001 5.05 0.06 2.38 0.01 Invention A2 0.36 0.17 0.51 0.0060.0003 5.04 0.06 2.34 0.01 A3 0.37 0.17 0.51 0.007 0.0001 5.06 0.07 2.400.01 A4 0.35 0.19 0.52 0.006 0.0003 5.08 0.06 2.35 0.01 A5 0.37 0.170.53 0.008 0.0002 5.11 0.06 2.38 0.01 A6 0.35 0.10 0.50 0.007 0.00024.98 0.06 2.33 0.01 H11 16X 0.39 1.06 0.41 0.006 0.0001 4.96 0.09 1.320.01 “Premium” H13  1X 0.40 1.10 0.41 0.008 0.0003 5.13 0.10 1.46 0.01“Premium” QRO 90  ® 14X 0.39 0.33 0.74 0.007 0.0003 2.64 0.07 2.29 0.01W.nr  4X 0.38 0.43 0.42 0.016 0.0004 5.08 0.09 2.84 0.03 1.2367 Com. 417X 0.37 0.30 0.35 0.006 0.0003 5.08 0.08 1.33 0.01 Com. 3 11X 0.36 0.210.57 0.007 0.0007 5.26 0.67 2.17 0.01 Com. 2 10X 0.36 0.34 0.56 0.0080.0005 5.03 0.09 2.55 0.01 Com. 1  9X 0.34 0.07 0.60 0.006 0.0014 5.460.07 2.94 0.01 Com. 5 18X 0.35 0.17 0.48 0.007 0.0048 5.19 0.07 1.630.01 Steel Steel O type No. Co V Ti Zr Nb Cu Al N ppm Fe A A1 0.02 0.570.002 0.001 0.001 0.04 0.008 0.007 5 Bal Invention A2 0.02 0.67 0.0020.001 0.001 0.04 0.016 0.007 4 Bal A3 0.02 0.57 0.002 0.001 0.001 0.040.038 0.007 5 Bal A4 0.02 0.55 0.002 0.001 0.001 0.06 0.015 0.008 5 BalA5 0.02 0.57 0.001 0.001 0.001 0.06 0.016 0.008 3 Bal A6 0.02 0.54 0.0020.001 0.001 0.04 0.017 0.007 6 Bal H11 16X 0.02 0.38 0.003 0.001 0.0020.06 0.07 0.009 7 Bal “Premium” H13  1X 0.02 0.92 0.004 0.001 0.002 0.060.031 0.008 6 Bal “Premium” QRO 90 ® 14X 0.02 0.83 0.002 0.001 0.0010.07 0.032 0.007 10  Bal W.nr  4X 0.02 0.66 0.003 0.003 0.001 0.06 0.0640.015 12  Bal 1.2367 Com. 4 17X 0.01 0.49 0.001 0.002 0.002 0.02 0.0050.013 6 Bal Com. 3 11X 0.57 0.86 0.002 0.003 0.001 0.03 0.005 0.025 13 Bal Com. 2 10X 0.03 0.63 0.002 0.002 0.001 0.05 0.020 0.018 8 Bal Com. 1 9X 0.01 0.83 0.003 0.002 0.001 0.05 0.017 0.013 10  Bal Com. 5 18X 0.010.45 0.002 0.002 0.001 0.04 0.011 0.012 20  Bal

In Table 2, H11 “Premium” and H13 “Premium” are variants of steel oftype AISI H13 and H11 respectively. “Premium” means that the steel meltsin connection with manufacture have been treated through SiCa injection,which brings about extremely low levels of sulphur content, and that thefinished products have undergone a modified hot working procedure. Thesteels are characterised, in comparison to standard steels of the sametype, by a higher level of toughness in all directions, greaterpotential to utilise higher hardness with maintained toughness andhigher thermal shock resistance.

Two heats were produced from steel of type A of the invention, and ofthese heats three ingots were produced by ESR remelting. These have beencalled A1, A2 . . . A6 in Table 2. The examinations described have beenprimarily concentrated on steel A2. In those cases when reference ismade to steel A, it is the matter of a mean value of the result of theexaminations of a greater number of the steels A1-A6. The meltmetallurgical treatment corresponded essentially with the processingapplied for H11 “Premium” and H13 “Premium”. The ESR heats had weightsvarying between 480 and 6630 kg. Bars were produced from these ingots ofvarious forms through forging and rolling.

The six last steels in Table 2, the steels 4X, 17X, 11X, 10X 9X and 18X,are materials that were acquired by the applicant on the market and thechemical composition of which have been analysed by the applicant.

All the steels, except QRO® 90 have a chromium content in the order of5%. Other steels examined differ from each other by varying contents ofprimarily silicon, molybdenum and vanadium. This is illustrated in FIG.1, which in the form of a three-dimensional coordinate diagramillustrates the nominal contents of silicon, molybdenum and vanadium ofthese steels. See Table 1 concerning the nominal contents.

The dimensions and also the hardness in softannealed state are indicatedby Table 3.

TABLE 3 Hardness in softannealed state Steel No. Dimensions (mm)Hardness (HB) A3 762 × 407 164 A3 762 × 305 162 A2 610 × 54 159 A2 610 ×203 164 A2 610 × 153 157 A2 508 × 127 163 A1 Ø508 163 A1 Ø350 156 A4 762× 407 174 A5 762 × 305 159 A5 700 × 300 163 A6 610 × 102 170 A4 Ø750 170A6 Ø270 170 A6 Ø125 170 A6 Ø80 170 16X 500 × 110 192 1X 762 × 305 17414X 356 × 127 174 4X 510 × 365 183 17X ˜500 × 200 164 11X 485 × 200 18910X 510 × 210 172 9X 510 × 210 207 18X 260 × 210 174

Structure investigations indicated that primary carbide content was zeroin all steels with the exception of steel no. 11X and 9X, whichcontained significant quantities of primary carbides and primarycarbonitrides. The microstructure in softannealed state in the centre ofthe steel no. A2, 610×203 mm, is shown in FIG. 2.

Tempering resistance after austenitizinc, at 1025° C./30 min. and alsothe influence of holding time at 600° C. after hardening 1025 ° C./30min (1010° C. for steel no. 16X) and tempering to 45 HRC is illustratedby the diagram in FIGS. 3 and 4. It is shown by these diagrams that thesteel of the invention A2 and steel 9X have the best temperingresistance. The steel A2 of the invention was also affected least by theholding time at 600° C., while steel no. 9X rapidly lost hardness. Thisalso applies to steel no. 10X.

Even hardenability was very good for the steel of the invention A2, asis shown by the CCT and TTT diagrams in FIGS. 5 and 6.

Toughness measurements were conducted as Charpy-V impact energy testsversus testing temperature and the results given in FIGS. 7 and 8respectively.

FIG. 9 shows the impact toughness at room temperature for unnotchedspecimens versus bar dimension. The curves illustrate that the steel ofthe invention, A2, has superior toughness and ductility among theinvestigated steels. It should be noted in particular that steel no. 4Xin FIG. 9 has been tested in TL1 direction, which gives 10% greatervalue than specimens taken in ST2 direction.

Hot tensile tests were conducted at 600° C. on specimens that had beenheat treated to 45 HRC. The results are shown in Table 4 and in FIG. 10.Even as regards this property, the steel of the invention hassignificantly better combination of high temperature strength andductility than the other steels investigated.

TABLE 4 Hot tensile properties after testing at 600° C. R_(p0.2) R_(m)A_(s) Z Steel no. Hardness (HRC) (Mpa) (MPa) (%) (%) A2 45.5 649 897 1780 16X 43.5 517 715 18 80 1X 44.5 584 795 17 83 11X 44.2 555 801 17 7810X 45.5 637 896 13 67 9X 45.2 615 897 14 67 18X 45.6 613 859 5 77

Certain critical properties of the invented steels are compared in thepolar diagram in FIG. 11. As regards toughness, the steels no. 11X and9X had high contents of primary carbides and carbonitrides, which havesignificantly reduced toughness for both of these steels. Steel no. 10Xand to a certain extent also steel no. 18X have a toughness that iscomparable with that of steel No 1X, but the steel of the invention, A2,has superior ductility and toughness. The latter also has been confirmedby full-scale press-forging tests. On these trials, which related toforging of large truck hub components, a steel of type H13 “Premium” andsteel A1 were used as tool material. The number of componentsmanufactured numbered 2452 and 7721 items respectively. The failure modeof H13 “Premium” tools comprised total failure, while the tools of A1steel were removed from service only as a result of plastic deformationof the die inner diameter.

The invention steel, A2, thus has the best yield strength, ductility(area reduction) and hardenability (in terms of hardness reduction). Thetempering resistance is also very good for A2. Among the investigatedsteels the invention steel, A2, has the best properties profile.

Without tying the invention to any particular theory, it can be assumedthat this superior properties profile may be the result of the followingfactors:

a balanced chemical composition of carbide forming elements such aschromium, molybdenum and vanadium aimed at, providing an excellentsoft-annealed initial structure for the subsequent tool hardening,thereby achieving a very good hardenability and good temperingresistance and high temperature strength properties,

absence of primary carbides and/or primary carbonitrides of MX typewhere M is vanadium and X is carbon and/or nitrogen, by optimal choiceof carbon and vanadium contents together with a low nitrogen content,

a comparatively high content of molybdenum, a relatively low content ofcarbon and a very low silicon content, which reduces carbon activity andthereby the tendency to precipitation of toughness reducing primarycarbides and grain boundary precipitations,

a low content of elements such as oxygen, nitrogen and sulphur, whichform toughness reducing oxides, nitrides and sulphides,

a low content of elements causing temper brittleness, such as phosphor.

What is claimed is:
 1. Steel material for hot work tools, characterisedin that it has an alloy composition that in weight-% essentiallyconsists of: 0.3-0.4 C 0.2-0.8 Mn 4-6 Cr 1.8-2.5 Mo 0.4-0.6 V balanceiron and unavoidable metallic and non-metallic impurities, said metallicimpurities comprising titanium, zirconium and niobium, which may bepresent in the following maximum amounts: max 0.01 Ti max 0.02 Zr max0.02 Nb and said non-metallic impurities comprising silicon, nitrogen,oxygen, phosphor and sulphur, which may be present in the followingmaximum amounts: max. 0.25 Si max. 0.010 N max. 10 ppm O max. 0.010 Pmax 0.010 S.
 2. Steel material in accordance with claim 1, characterisedin that it contains max. 0.20 Si.
 3. Steel material in accordance withclaim 1, characterised in that it contains max. 0.0010 S.
 4. Steelmaterial in accordance with claim 1, characterised in that it contains:0.33-0.37 C 0.4-0.6 Mn, and 4.5-5.5 Cr.
 5. Steel material in accordancewith claim 4, characterised in that it contains 4.85-5.15 Cr and 2.2-2.4Mo.
 6. Steel material in accordance with claim 1, characterised in thatit contains max. 0.008 N.
 7. Steel material in accordance with claim 1,characterised in that it contains max. 8 ppm O.
 8. Steel material inaccordance with claim 1, characterised in that it contains max. 0.008 P.9. Steel material in accordance with claim 1, characterised in that itcontains max. 0.0008 S.
 10. Steel material in accordance with claim 1,characterised in that it contains 0.35 C, max. 0.15 Si, 0.5 Mn, max.0.0008 S, 5 Cr, 2.3 Mo, 0.55 V, max. 0.008 N, max. 8 ppm O.
 11. Steelmaterial in accordance with claim 1, characterised in that it containsmax. 0.008 Ti, max. 0.016 Zr, and max. 0.010 Nb.
 12. Steel material inaccordance with claim 1, characterised in that it contains 0.5-0.6 V.